Spurious emission of Tx is troublesome for any RF-ASIC design. The RF-ASIC for the multi-band multi-standard, e.g. mobile phones, contains more than one Tx and Rx with multiple VCO, which makes the situation for spurious emission very complex. The problem is severe for mobile phones with multi-band multi-standard radio AISC. In such RF-ASICs the occurrence of spurious emission in the band of interest is very common and thus causes problems.
As the fabrication technology for Integrated circuits (IC) shows lower and lower production costs, the total cost of Application Specific Integrated Circuits (ASIC) nowadays mostly depends on design, verification and characterization time rather than production cost itself. Radio Frequency (RF) ASIC is one of the densely integrated systems-on-chip (SoC), containing transmitter (Tx), receivers (Rx) and corresponding local oscillators (LO) and voltage controlled oscillators (VCO), clocks and digital blocks.
In attempts to solve the problems related to the spurious emission a first step have been to identify or predict the spur frequencies. For a simple mixer, the spur frequencies can be predicted very easily from local oscillator (LO) and baseband (BB) signal. However, for multi-standard radio, much more calculations or careful measurements are needed in order to identify and eliminate spurs. Several methods and articles are available to describe spur elimination method for BB signals. Some articles also addresses spur issues for multi-band signals such as pattern generator or satellite TV where the carriers are in periodic distance with single LO. The spur search time for a multi-standard radio will be a multiplication of the total combination number of operational modes and the measurement time for a single mode. During the carrier aggregation for Long Term Evaluation (LTE) mode, the number of combinations increases more. For a single operational mode in single band of a TRx of a RF-ASIC the spur search time depends on bandwidth (BW), noise-level, Resolution Bandwidth (RBW).
US 2011/0103431 discloses interference cancellation in a multi-standard receiver. All possible spur frequencies are measured separately. The method includes receiving a signal of a second radio technology with interference from a transmission signal of a first radio technology, translating the interference into a narrower frequency band to obtain a received signal with narrowband interference, and filtering the received signal with narrowband interference to obtain a signal without the interference.
U.S. Pat. No. 8,121,573 discloses a multi-standard communication system including the aspect of determining spurs. It discloses methods and systems for coexistence in a multiband, multi-standard communication system utilizing a plurality of phase locked loops (PLLs). Aspects include determining one or more desired frequencies of operation of a transceiver, determining a frequency of unwanted signals such as spurs, intermodulation, and/or mixing product signals, and configuring the PLLs to operate at a multiple of the desired frequencies while avoiding the unwanted signals. The desired frequencies may be generated utilizing integer, which may include multi-modulus dividers. The wireless communication standards may include LTE, GSM, EDGE, GPS, Bluetooth, WiFi, and/or WCDMA, for example. The frequencies may be configured to mitigate interference. PLLs may be shared when operating in TDD mode, and used separately operating in FDD mode. One or more digital interface signals, zero exceptions on a transmitter spur emission mask, and sampling clocks for ADCs and/or DACs in the transceiver may be generated utilizing the PLLs. In an exemplary embodiment, there may be three different filter types and eight different filter cutoff frequencies in the filter. Further, the use of Tx spur masks is mentioned.
A problem is that very little information is available for the multi-band TRx for multi-standard radio where the carriers are not periodic, the signal strengths are not equal and there is presence of multiple clocks and LOs. The process of spur search is a very tedious work which leads to longer design cycle of TRx with low test coverage. A known spur search method for equally spaced carrier in a multi-tone system is dependent on the greatest common divisor (GCD) of the tones. This known method however cannot be used to detect spur in a multi-band multi-mode non-periodic signal as the greatest GCD can be smaller than the resolution bandwidth (RBW). Further, no known method addresses how to reduce time spent on spur search measurement.
Using conventional method of linear scan for spur will not help to simulate or measure all bands or all modes of operation for each transmitter. Thus there will be a huge uncovered area in characterization for a designed RF-ASIC which adds a huge risk. Also to increase the coverage the measurement/simulation time of the TRx Design will be huge and the design cycle will longer and economical not viable.
In order to speed up the design cycle of RF-ASIC thus there is a need for an improved method for spur frequency prediction, detection and elimination. Further, there is a need of an improved method in the case that the spur finding process needs to be implemented by a Built-In-Self Test (BIST) for performance enhancement of the mobile communication.